LONDON (AP) -- Most people send a card, call, or post on Facebook for someone's birthday, but President Barack Obama went the extra mile on Friday -- thousands of miles, actually --  to deliver 90th birthday greetings to Queen Elizabeth II over lunch at Windsor Castle.

Britain's oldest and longest-serving monarch celebrated her birthday a day earlier, the same day Obama arrived in the evening for what likely is the final visit here of his presidency. So the two heads of state sat down for an only slightly belated birthday lunch at the castle, west of London.

Obama's wife, Michelle, flew in from Washington to attend the royal engagements. The queen's husband, Prince Philip, was on hand as well.

The queen put a scarf over her head and came out in a light, drizzling rain to greet the president and first lady as their helicopter landed on the lush green lawn outside the castle. The couples shook hands warmly before hopping into a black Range Rover, driven by Philip, to head back to the castle. Obama sat in front with Philip, the queen and the first lady in the back seat.

A few minutes later, the queen led the four into a sitting room with a roaring fire, and asked the president where he'd like to sit.  The four posed for pictures before the private lunch. The queen was dressed in a light blue suit; the first lady wore an Oscar de la Renta print dress and a black Narciso Rodriguez coat.

Later, Obama planned to have dinner with Prince William, his wife Kate and brother Prince Harry at the younger royals' Kensington Palace home in central London. William is second in line to inherit the British throne after his father, Prince Charles.

Obama was breaking up his royal holiday with a stop at 10 Downing St. for talks with Prime Minister David Cameron about the multinational campaign against the Islamic State group, as well as counterterrorism efforts, Afghanistan, Syria, Libya, the global economy, Russia's stance toward Ukraine and other issues.

Political issues in the United Kingdom and the U.S., including Britain's possible exit from the European Union, or Brexit, are on the agenda, along with the U.S. presidential campaign that will determine Obama's successor.

Cameron is leading the campaign in favor of Britain's continued membership in the 28-nation EU, which Obama also supports. He wants Obama to speak out against severing ties, but voters will have the final say in a June 23 referendum. Cameron faces opposition from within his own Conservative government and widespread skepticism among voters about the benefits of staying in the EU. Backers of those who support Britain's exit, meanwhile, have accused Obama of hypocrisy and interference.

In an opinion piece published online Thursday by the Daily Telegraph newspaper, Obama urges Britons to stay in the EU. He notes the decision will affect U.S. interests and says "The U.S. and the world need your outsized influence to continue - including within Europe."

Another issue that could come up is Obama's criticism of Cameron in an interview published recently in The Atlantic magazine. In the article, Obama faulted Cameron and other European allies for shortcomings in their handling of Libya after the 2011 toppling of leader Moammar Gadhafi. Obama said Cameron had become "distracted" by other issues.

Libya has since descended into chaos and become a haven for members of the Islamic State group.

Obama's lunch with the queen is the latest in a series of engagements between the two families since he took office in 2009.

"Each time, the president has come away with an even deeper personal affection for her,'' said Obama spokesman Josh Earnest. "She is an important symbol of a country with whom the United States has a special relationship. But she also is a human being whose charisma and a sense of nobility and honor is something that I think people around the world are attracted to."

Obama described the queen as "delightful" following their first meeting in 2009. He also told an aide that she reminded him of his grandmother.

That meeting is also where the queen and the much-taller Mrs. Obama showed how quickly they took a liking to each other by briefly standing arm in arm at a Buckingham Palace reception for world leaders attending an economic summit in London. The queen strayed from protocol by wrapping an arm around the first lady, who reciprocated.

A palace spokesman at the time described the scene at the ladies' first meeting as a "mutual and spontaneous display of affection."

The queen subsequently hosted Obama for a state visit in May 2011, during which the president and first lady slept at the palace. Obama and the queen also met in June 2014 during ceremonies marking the 70th anniversary of the D-Day landings in Normandy, France.

Prince Charles and his wife, Camilla, and William and Harry, have all visited Obama in the Oval Office.

Harry, a military veteran who served in Afghanistan, joined Mrs. Obama for a White House event in 2013. In 2015, they met at a U.S. military base to highlight their shared interest in the needs of military families and wounded service members. She and daughters Malia and Sasha also sipped tea with Harry at Kensington Palace when the first lady stopped in London last year.